EDM is a well-known and widely used machining technique. It operates through the erosion of a workpiece, generally metallic, through electrical discharges from an electrode. The process takes place in the presence of a liquid dielectric fluid, such as de-ionized water. An electrode in the shape of an elongated rod, thin wire, or shaped article is put into close contact with the workpiece. Through an electrical potential difference, arcing occurs between the workpiece and the electrode which causes erosion of the workpiece material in a desired manner.
EDM processes are used in numerous machining applications. It is especially desirable for its high forming accuracy, the ability to machine extremely hard workpieces, its low applied loading of the workpiece, and its ability to form deep bores in workpieces.
During the EDM machining cycle, it is necessary to precisely position the end of the electrode with respect to the workpiece surface being machined as erosion of the workpiece occurs. Due to sacrificial material loss of the electrode, it is also necessary to incrementally advance the electrode tip with respect to the workpiece. Since EDM machining requires maintenance of a critical gap between the electrode and workpiece surface, the positioning of the electrode is provided by precision servo motor heads. A closed loop control system continuously monitors electrical parameters associated with the arc discharge and continuously controls the position of the head to move the electrode with respect to the workpiece.
Currently available EDM systems typically utilize a servo motor positioning head using a lead screw type actuator. A precision servo motor rotates the lead screw which causes the head position to be incrementally moved. The present systems have several significant limitations. There is typically a trade-off between the precision of positioning provided by a head and the speed at which it can be moved. The ability to quickly move the head into a machining position and withdrawing from it, while permitting highly accurate positioning is a desired attribute.